If you open a restaurant specializing in one or two things, you'd better get those one or two things right. And if your name is Robert Wiedmaier, you have to know that expectations are going to be higher for you than for a garden-variety chef.

Wiedmaier is the 50-year-old impresario behind a handful of restaurants in the area, foremost the civilized and luscious Marcel's in Washington's West End, but also the more rollicking Brasserie Beck downtown and the neighboring Brabo and Tasting Room in Alexandria. A fixture on the restaurant scene for the past 25 years, he's considered one of the city's better cooking talents.

You wouldn't know that from dipping into Mussel Bar by RW, his new eatery in Bethesda. While I thrilled when the project was announced last December -- the chef whetted my appetite with plans to resurrect one of his youthful lively haunts off the Grand Place in Brussels in a "slam-dunk location" in Maryland -- the bricks-and-mortar reality tastes DOA. The dining room is cramped, the tables are too small, and much of what lands on them is listless. As for the sound level, it's beyond boisterous. I've never left Mussel Bar without a headache from the noise.

Or the feeling that this is a giant ATM with a dishwasher, and I'm getting ripped off. "What's light and refreshing?" I overhear a beer fan ask a bartender. She responds with 10 ounces of a Gouden Carolus Hopsinjoor, with a nice bite in its finish. But it's also priced as if by the Ritz at $12. Note to servers everywhere: If you're asked to recommend something for a customer, you should get some sense of how much he or she wants to spend, or at least specify an item's cost.

Warning signs appear early, starting with big but clumsy salads, and flatbreads that run to crackery crusts topped with a glop of Gruyere and chunks of uber-fatty pork belly and too few (and shriveled) mussels.

The kitchen, inattentively watched over by chef Robert Gadsby, wholly disrespects oysters. The first time I ordered a plate of raw ones, they came to the table pre-dressed in rice wine vinegar and peppers, a transgression a seafood purist might liken to finding A1 sauce on a steak. The replacements were no better: They were devoid of the oyster liquor that makes eating fresh oysters such a delight. (Wiedmaier encourages traditionalists to announce themselves if they want 'em briny.) The fried oysters are even worse. Mine were encased in what tasted like cardboard, and they were so big and flat, they appeared to have been run over by a steamroller. The accompanying sweet pink dip only hastened my retreat.

Mussel Bar misses its own point, often overcooking its small and surprisingly bland Prince Edward Island mussels, available in 10 or so sauce combinations. (At press time, Wiedmaier was exploring a switch to Penn Cove mussels from Washington state.) The bivalves arrive in a big, round pan whose lid is lifted at the table, releasing a cloud of steam and aromatics. Of the several combinations I've sampled, the best has been a straightforward sauce of tomatoes, basil and capers, the aptly named Provencal. A watery special composed of goat cheese and salami, however, left only a vague impression on the tongue.

The restaurant doesn't make its own french fries, by the way. Wiedmaier says it pained him not to serve french fries cut by hand, something that eventually proved impractical when he tried it at Brasserie Beck, given the volume of potatoes the restaurant served. It pains this food lover to waste calories on the solution Wiedmaier turned to: a frozen product imported from Canada that doesn't taste much like potato. A mussel joint shouldn't cut such a significant corner. To fill up here, you might find yourself mopping up one of the more agreeable sauces with some bread -- provided you get any.

A waiter underplays one of the sandwiches we ask about, but we take a chance and order roast beef with Chimay cheese anyway. Shame on us for not listening. The thinly cut meat and its inconsequential roll have next to no flavor; the only taste we can detect is that of the Belgian cheese. Mediocrity infuses the specials, too, which are listed on a big chalkboard above the circular bar. Among the disappointments were sticky-sweet, less-than-meaty "Thai" ribs that came with a potato salad thrown together with unwieldy chunks of tuber and a gloppy yellow binder.

There's a modest attempt to make the dining room, which is cleverly illuminated with a "chandelier" fashioned from empty wine bottles, look as if there's a personality attached to the business. In one of the few soft touches, the walls behind the lantern-lit booths in the dining room display photographs of Wiedmaier playing with his sons and riding his cherished motorcycle.

But by dessert, I'm ready to escape this boom box. The brief and boring selections give me no reason to linger, anyway.

The hero of this story is Thor Cheston, Beck's general manager and the man behind Mussel Bar's beer list and its dozens of pilsners, stouts and India Pale Ales from around the world: liquid relief from the endurance contest that is Mussel Bar. A food-loving friend who went once and vows not to return put it best: "I was at least expecting Beck's Light, so to speak."